Mail sends from localhost but not from live site on digital ocean

Question

I am using the Sendgrid API to send emails from my Node.js project. When running on my local machine this works just fine but now I have deployed to Digital Ocean (Ubuntu) the mails do not send. I have read that Digital Ocean blocks smtp ports by default and you can apparently open them through the command line but I can't find an easy to understand explanation on how to do this.

const nodemailer = require("nodemailer");
const sendgridTransport = require('nodemailer-sendgrid-transport');

    const transporter = nodemailer.createTransport(sendgridTransport({
      auth: {
          api_key: process.env.SENDGRID_API
      }
    }));

    return transporter.sendMail({
      to: '[email protected]',
      from: email,
      subject: subject,
      html: `<h1>Contact Form</h1>
            <p>Name: ${name}</p>
            <p>Email: ${email}</p>
            <p>${comments}</p>
    `
    });

UPDATE

If I remove the .env for the api key and actually hardcode it in eg:

const transporter = nodemailer.createTransport(sendgridTransport({
  auth: {
      api_key: '12345677788999'
  }
}));

then my emails send. This is my .env file ( I am using dotenv)

DB_USER=username
DB_PASSWORD=password
DB_NAME=mydbname
SENDGRID_API=12345677788999

So, not sure why that would be?